How effective are underride guards?

How effective are underride guards?

A recent report published by the National Highway Traffic Safety Administration indicates that the stronger underride guards mandated for trailers have had limited effect in reducing deaths and serious injuries. The technical report, “The Effectiveness of Underride Guards for Heavy Trailers,” says that based on limited crash data, the guards appear to help when passenger cars crash into them, but the research data do not support a statistically significant difference. NHTSA is requesting comments by March 8, 2011.

Safety Standards 223 (49 CFR 571.223) and 224 (49 CFR 571.224) require underride guards meeting a strength test on trailers with a GVWR of 10,000 pounds or greater manufactured on or after January 24, 1998. Safety Standard 224 defines the size requirements for the guards, while Safety Standard 223 describes strength testing and energy absorption requirements for DOT-compliant guards.

The report is a statistical analysis of crash data aimed at determining the effectiveness of standard-compliant underride guards at preventing fatalities and serious injuries in crashes where a passenger vehicle impacts the rear of a tractor-trailer.

The primary findings:

Data from Florida and North Carolina showed decreases in fatalities and serious injuries to passenger vehicle occupants when rear-ending a tractor-trailer subsequent to the implementation of Safety Standards 223 and 224. However, the observed decreases are not statistically significant at the 0.05 level, possibly due to the small sample sizes of the data. Using supplemental data collection from North Carolina, it is shown that passenger vehicle passenger compartment intrusion is more apt to occur when the corner of the trailer is impacted, rather than the center of the trailer. This result is statistically significant at the 0.01 level.

“It is not possible to establish a nationwide downward trend in fatalities when a passenger vehicle rear-ends a tractor-trailer—neither in terms of total number of fatalities, percentage of fatalities in rear impacts relative to other passenger vehicle fatalities involved in tractor-trailer accidents, nor number of fatal crashes per 1,000 total crashes,” NHTSA says in the report. “The Fatality Accident Reporting System does not list the model year of the trailer.”

In April 2009, NHTSA issued An In-Service Analysis of Maintenance and Repair Expenses for the Anti-Lock Brake System and Underride Guard for Tractors and Trailers (74 FR 18803).

The new technical report is available on the Internet for viewing in PDF format at http://www-nrd.nhtsa.dot.gov/Pubs/811375.pdf. A copy of the report free of charge can be obtained by sending a self-addressed mailing label to Charles J. Kahane (NVS-431), National Highway Traffic Safety Administration, Room W53-312, 1200 New Jersey Avenue, SE., Washington, DC 20590. Comments (identified by Docket Number NHTSA-2010-0150) can be submitted at http://www.regulations.gov.

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